The invention relates to the field of vehicle engines. It relates more particularly to detecting the malfunction of the circuit of a gasoline vapor filter (canister) which is fitted in vehicles provided with a gasoline internal combustion engine.
For several years now and for the purpose, amongst other things, of reducing pollution generated by vehicles having a gasoline engine, and at the same time for the purpose of reducing the fuel consumption thereof, fuel tanks of said vehicles are provided with a device for recovering gasoline vapors which reinjects said vapors into the engine. This device, usually denoted the “canister” by the person skilled in the art, is arranged in the vicinity of the gasoline tank. It comprises a carbon filter which fixes the gasoline vapors, in particular when the engine is at a standstill. The injection of the vapors into the engine via the inlet duct is controlled by the electronic control unit of the engine or ECU (Engine Control Unit) permitting the opening and the closing of a bleed valve.
Current standards in some countries make it necessary to be able to detect the presence of a leak of gasoline vapors from a vehicle. This involves diagnosing any possible leaks and the malfunction of the components involved, in particular the gasoline vapor filter (canister) and the bleed valve.
Methods are known in the prior art for detecting the operation of the bleed valve using a test carried out when the vehicle is at an idle speed. In said methods, a series of openings and closings of the bleed valve are controlled over a period of approximately ten seconds. If the valve is operational, the admission of the mixture from the gasoline vapor filter into the engine has to result in the modification of various operating parameters, such as the torque, the engine speed, the intake pressure, etc. Thus it is detected if one of these parameters, which may depend on the vehicle under consideration, varies beyond a predetermined threshold, and this variation then validates the correct operation of the bleed valve of the vapor filter. Such a method is, for example, disclosed in the patent application FR 2 900 981 from Siemens VDO Automotive.
It is clear that this technique is not applicable in the case of engines using an ignition control method called “start stop” which cuts out the engine each time the vehicle is at a standstill, and as a result suppresses the idle phase of the engine. Similarly, this method is not conceivable for vehicles using a hybrid-type engine, combining an internal combustion engine (ICE) and an electric motor/generator. More specifically, said hybrid engines operate in electrical mode at low speed and thus do not have an idle engine speed permitting the verification of the operation according to the principle cited above.